The present invention relates to apparatus for controlling the yarn guides of multifeed circular knitting machines by means of pneumatical and mechanical means.
Circular knitting machines are known, in which yarn is fed to the needles through yarn guides and cams which are movable between operative and inoperative positions by pneumatic means. In general, the yarn guides are controlled by a piston mounted in a pneumatic cylinder which acts against a spring. Thus, the yarn guide is controlled into its operative, or inoperative position, respectively by either introducing or not introducing a pneumatic signal first into the cylinder. During its stay in operative position the yarn guide held there by the piston under a continuous injection of pressurised air to the cylinder. The pressurized air is fed to the guide from a source via a central distribution valve controlled from a control drum of the machine.
The known pneumatic devices operate as a whole reliably. However, they do have a disadvantage consisting in that it is necessary, in order to maintain the yarn guide in operative position, to maintain constant pressure in the pressurized air feeding duct. Thus, it is necessary to manufacture the pneumatic cylinder, in which the piston is mounted with a high degree of precision, and to seal the piston very accurately so as to avoid air losses and pressure drop, which if allowed to accrue would cause the guide to move from its correct operative position. Laying of yarn would be performed at an incorrect angle and the knitwork structure could become faulty.
It is an object of the present invention to provide apparatus for controlling the movement of yarn guides which overcomes the above mentioned disadvantages.
It is another object of the present invention to form a pneumatic device operating in response to a short duration pressure impulse without any pressure drop.
It is a further object of the present to provide a device consisting of two alternately controlled resilient pistons arranged for controlling at least one guide into both its operative and inoperative position.
The foregoing objects, other objects and advantages will be obvious from the following disclosure.